Circuit arrangement for the formation of a signal from a plurality of other signals



Aug. 28, 1962 J. KAASHOEK ETAL 3,051,912

CIRCUIT ARRANGEMENT FOR THE FORMATION OF A SIGNAL FROM A PLURALITY OFOTHER SIGNALS Flled Aug 15, 1958 3 Sheets-Sheet 1 INVENTORS JOHANNESKAASHOEK TEUNIS POORTER AGENT Aug. 28, 1962 J. KAASHOEK ETAL 3,051,912

CIRCUIT ARRANGEMENT FOR THE FORMATION OF A SIGNAL FROM A PLURALITY OFOTHER SIGNALS Filed Aug. 15, 1958 3 Sheets-Sheet 2 JOHANNES KAASHOEK TEUNIS POOR TER BY M 2. 3.2.

AGEN

1962 J. KAASHOEK ETAL 3,051,912

CIRCUIT ARRANGEMENT FOR THE FORMATION OF A SIGNAL FROM A PLURALITY OFOTHER SIGNALS Filed Aug. 15, 1958 5 Sheets-Sheet 3 FI (S59 INVENTOR SJOHANNES KAASHOEK TEUN IS POORTE R United States Patent CIRCUITAFRAIQ'GENENT 1 0R THE FORMATIGN OF A SIGNAL FRQM A PLURALHTY 0F @THEREGNALS Johannes Kaashoelr and Tennis Poorter, Eindhoven,

Netherlands, assignors to North American Philips Company, Inez, NewYork, N.Y., a corporation of Delaware Filed Aug. 15, 1958, Ser. No.755,327 Claims priority, application Netherlands Aug. 27, 1957 4(Ilaims. (Cl. 330-69) The invention relates to a circuit arrangement forthe formation of a signal from a plurality of other signals, the formedsignal is linearly dependent upon the forming signals.

Such circuit arrangements are employed, inter alia in radio andtelevision studio apparatus, in which a plurality of signals originatingfrom microphones or television cameras are fed to a so-called matrixcircuit, the output signal of which is linearly dependent upon thesignals supplied thereto.

In certain cases, the coelficients determining the said linearrelationship may be varied, so that, in the formed signal, certainsignals are more pronounced than the others.

In colour television arrangements, in which a correction signal is to beformed with the aid of the so-called brightness signal, the problemarises that, in view of this correction, it is not sufiicient for thevarious coefiicients which determine the linear relationship in thisbrightness signal to be varied separately, there must, moreover, be adefinite linear relationship between the coefiicients themselves, sinceotherwise an erroneous correction is obtained, if neutral white or greyis to be reproduced. This would be particularly undesirable with abright white signal with maximum amplitudes of the composing coloursignals.

The circuit arrangement according to the invention provides a solutionfor this problem and is characterized in that the arrangement comprisesimpedances having displaceable tappings, in which arrangement the saidsignals being fed to the terminals of the impedances, the signalobtained from a tapping being supplied to the controlelectrode of anamplifying element, whilst to at least one further amplifying element issupplied either a signal obtained from a different tapping or the sum ofthe forming signals, supplied with a given strength, the combined signalobtained from the outputs of the amplifying elements being a linearcombination of the forming signals, in which combination thecoefiicients determining this linear relationship are variable by meansof the said tappings and with the aid of means provided in the outputsof the amplifying elements in such a manner between 0 and 1 that,irrespective of the positions of the said tappings, their sum remainsequal to 1.

A potential embodiment of the arrangement according to the inventionwill be described with reference to the figures.

FIG. 1 shows a first embodiment;

FIG. 2 serves for explanation;

FIG. 3 shows a second embodiment;

FIG. 4 shows the total circuit arrangement in the practical embodiment,and

FIG. 5 shows an arrangement extended in accordance with the principleillustrated in FIG. 1.

FIG. 1 shows a so-called variable matrix arrangement for use in athree-colour television system, in which, for example V designates thered signals, V the green signal and V the blue signal.

It is known that with the reproduction of colour television signals,apart from the conventional gamma corrections, which relate to thenon-linearities of the reproducing tubes, additional corrections can becarried out, whilst the total brightness signal V which is composed ofthree colour signals in accordance with the formula wherein oz, [3, and6 represent proportionality constants varying with the system employed,is used to form a correction siganl, which is a function of thisbrightness signal. After multiplication of this formed signal by thecolour signal to be corrected, and if the contrast region to be recordedis larger than that covered by the reproducing apparatus, a correctedsignal may be obtained, of which the exponent power must be lowerthan 1. If, on the contrary, the contrast region to be recorded issmaller than that covered by the reproducing apparatus, the powerexponent of the corrected signal must exceed 1.

If for the signal formed from the brightness signal V a signal of theform:

is chosen, signals will be produced of the form g ul K Herein (l-n) isthe aforesaid power exponent. In the first-mentioned case (ln) must besmaller than 1, so that to It must apply: O n 1, wherein, in accordancewith the additional brightness signal desired, It can be chosen to behigher or lower within the said range.

In the second case it must obtain that: 1-n. 1, so that it must be 0;also in this case the desired additional correction determines thechoice of n.

It should be noted that the normal gamma correction may be carried outboth prior to and after this additional correction. Only when stronglysaturated colours prevail, deviations occur in the first-mentioned case,which, however, exert a negligibly low influence, as is evident from acalculation.

This brightness correction is not only important for the matching of thecontrast regions, but also in those cases in which, for eXample a filmis to be scanned and reproduced in a television reproducing apparatus.This film may have a 'y l, which can be compensated by the aforesaidmethod.

Also in those cases in which the brightness of the dark image parts isto be pronounced against the bright parts, this method is advantageous.

However, this brightness correction has the following disadvantage.Assuming that the green and the blue signal are very small for a givendetail of the total image to be reproduced, We may write for thebrightness signal, with a certain approximation:

3 F Subsequent to correction a signal:

VIII

1 1-): Vt) ir) is obtained.

Now n is only the determining factor, which means, since n is fixed forthe correction of the image concerned, that the red colour as suchcannot be touched up in the image detail concerned, which may bedesirable in certain cases. The same applies, of course, to an imagedetail having more or less saturated green and blue and also tocombination signals, in which given colour components are to be touchedup addition-ally.

There should therefore be means to vary separately the coeflicients a,,6 and a, whilst yet with a neutral colour the correction signal remainsequal to the correction signal, of which the coeflicients have not beenvaried, so that the correction of this neutral signal does not dependupon the separate colour correction. If, in the aforesaid case, forexample the cc of the correction signal is rendered smaller, this meansthat the brightness of the red details in the image to be reproduced ispronounced. It may be said, as a rule, that the brightness of thosecolour details is emphasized, of which the coefficientts) for theco1our(s) concerned in the correction signal is (are) reduced.Conversely, as a matter of course, the brightness of those colourdetails is reduced, of which the coefficient(s) for the colour(s)concerned in the correction signal is (are) raised. With complex signalsno colour distortion occurs, since, as it follows from Equation 2, thecorrection signal is multiplied by the three colour signals, so that therelative ratios are maintained. The arrangement shown in FIG. 1 providesthe possibility of composing the desired correction signal.

To the potentiometer 12 between the points 1 and 2, are fed the signal Vsupplied by the signal source 9 with its internal resistor 6, and thesignal V supplied by the signal source 11 with its internal resistor 8.If the resistance value of the resistors 6 and 8 is small with respectto that of potentiometer 12 and if the resistance value between thetapping and point 1 is a fraction 7 of the total resistance value, thevoltage at point a of the switch 20 will be:

Also the blue signal supplied by the signal source with its internalresistance 7 is fed to point 3. In a similar manner as stated above thevoltage at point b is given by It should be noted that a satisfactoryoperation of the arrangement requires that with equal amplitudes of thesignals V V and V also the amplitudes of the signals at points 1, 2 and3 should have the same value.

In accordance with the position of the switch 20, the main contact ofwhich is connected to the conductor 18, one of the signals according to3, 4 or 5 is fed via the conductor 18 to the control-grid of thedischarge tube 16. Moreover, the total brightness signal V is fed to thecontrol-grid of the tube 17 If R R and R R and if the switch connectsthe conductor 18 to point a, the voltage across the conductor 19 can berepresented with some approximation by:

r+fig+ b wherein it is assumed that the resistance value between thetapping of potentiometer 45 and point 5 is a fraction 5 of the totalresistance value. Also in this case a satisfactory operation of thearrangement requires that the amplitudes of the signals at points 4 and5 should be equal to each other.

If point bis connected to conductor 18, it is found that:

and for point 0:

The new correction signal V replaces, for the brightness correction theinitial signal V The additionally corrected signal then becomes:

1 i W H From 6, 7 and 8 it follows that with the aid of the coefiicientse, 'y 72 and 7 each desired ratio between the colour components can beadjusted. Yet, in the case in which the amplitudes of the signals areequal to one another, i.e. with a neutral colour, the correction signalremains equal to the correction signal obtained without the possibilityof varying the coefficients. If it is assumed that V '=V =V =V itfollows from 6:

since, for each colour television system obtains that w+;3+5=1, it isfound therefrom, irrespective of the value of e and 'y so that 9 changesinto:

VII!fiW (Vw)1n If use had been made of the correction signal V thenV1j=Vw, so that the same result is obtained.

For a bright white signal V =l, so that the exponent (l-n) does nolonger affect the signals, which are therefore not corrected.

The same applies to the Formulae 7 and 8, so that, irrespective of thepositions of the itappings on the potentiometers 12, 13, 23 and of theswitch 20, With a neutral colour the correction is not varied, or withmaximum white no correction at all occurs. This is due to the fact that,irrespective of the positions of the tappings, the sum of thecoefficients remains equal to 1.

FIG. 2 illustrates by means of a colour triangle the region covered bythis arrangement. Herein 123 designates the point which is the initialbrightness signal V The lines from this point to the triangle sides 12,13, 23, i.e. to the points determined by the positions of the tappingson the potentiometers 12, 13 and 23, can be covered by a variaion of eand by a variation of the 7 values these lines can be displaced so as tocoincide with the lines of the triangle connecting the corners with thepoint 123. The latter are indicated as broken lines in FIG. 2. Byvariation of '7 and 6 between 0 and 1, the region associated with thetriangle 1, 2, 123 can be covered and similarly by variation of '7 ande, the triangle 1, 3, 123 and fiinally by variation of 'y and e theremaining part of the triangle 1, 2, 3.

As a rule, it can be stated that the desired hue correction can beadjusted by means of the 7 values and the saturation correction by meansof the 6 values, so that the direction and the degree of correction arecompletely controllable.

FIG. 3 shows a second embodiment, in which corresponding elements aredesignated as in FIG. 1. The switch 20 is omitted, but replaced by arunning contact 21, which is slidable along the three joined resistors12, 13 and 23, so that it determines the adjustment of the coefficients7 v and This has the advantage that the arrangement can operate with oneinstead of three control-members. To the points 1, 2 and 3 are again fedthe signals V V and V A practical embodiment of the complete arrangementis shown in FIG. 4, in which corresponding parts are designatedcorrespondingly as far as possible. According to this figure the yes orno normal gamma corrected signals V V and V are fed via the networks ofthe resistors 32, 33, 34 for the signal V 35 and 36 for the signal V and37, 38 for the signal V to the control-grids of the tubes 26, 27 and 28.These tubes produce, across the cathode resistor 29, a signal which isobtained, by means of the tapping 31 adjusting the signal to the desiredvalue, from the resistor 30, which is connected in parallel with theresistor 29. The signal at tapping 31 had the form:

wherein K designates a proportionality factor which varies with theemployed resistors and with the position of the tapping 31. To the tubes22, 24 and 25, which replace in this arrangement the voltage sources 10,11 and 9, respectively, are fed the signals K V K V and K V (wherein Kdesignates a proportionality factor) so that across the resistors 39, 40and 41 are produced signals, which can be obtained in the mannerdescribed above from the resistors 12, 13 and 23. The further part ofthe arrangement is, with the exception of the networks for the tubes 16and 17, identical to that shown in FIGS. 1 and 3 and is selfexplanatory. Also in this case a satisfactory operation requires thatthe amplitudes of the signals at points 1, 2 and 3 should have the samevalue and also those at points 4 and 5.

With a practical embodiment as shown in FIG. 4 the proportionalityfactors are:

:03; ,B=0.6 and 5:0.1

The resistors are in this case:

12 :4109; R 5=R =R =R 1000s With these resistance values the signals fedto the tubes 26, 27 and 28 are: V V and /2 V respectively, whilst thesignals fed to the tubes 22, 24 and 25 are: /2 V /2V and /2 V so that K=0.5. The tubes 22, 24 and 25 are connected as cathode-followers, sothat the voltages at points 3, 2 and 1 are attenuated by a factor ofapproximately 0.6. The voltages at these points then become: 0.3 V 0.3 Vand 0.3 V By adjusting the tapping 31 in a manner such that the totalsignal across the resistors 29 and 30 is multiplied by about 0.18, thetotal output signal becomes:

The proportionality factor K thus amounts in this arrangement to about0.3.

It will be obvious that the use of this variable matrix circuit is notrestricted to the use as a forming circuit for the formation of thecorrection signal V With the aid of this arrangement a new combinationsignal may be produced, the coeflicients of which can be varied inaccordance with the requirements. If, for example, formula (7) isrewritten, we obtain:

wherein 3 o and may be varied, at will, between the values 0 and 1. Thuscolour dilation in the reproduced picture can be corrected whenreproducing tubes having different kinds of phosphors are used. In thiscase 5 5 must always be equal to 1, which is fulfilled with eachadjustment, if it obtains that a+fi+=l.

A further extension of the arrangement is possible by increasing thenumber of signals, the number of potentiometers and the number ofcontacts of the switch 20. FIG. 5a shows an arrangement according to theinvention, in which four signals V V V and V; are fed to four angularpoints of a network. This network is built up of six tappedotentiometers, which tappings are connected 6 to the six contacts a to fof the switch 20. To the tube 17 is fed the complex signal If the switch20 occupies the position shown, the signal V is found to be:

wherein it obtains that:

11-l- 72-l- 1a-l- 14.=

from which follows that: for V =V =V =V =V: V V, irrespective of thepositions of the tappings concerned. The same applies to the signalsobtained, if the switch 21) connects a different contact to theconductor 18.

For a: 1, we can obtain a signal consisting of the combination of two ofthe four composing signals. For the case shown in FIG. 5a, this becomes:

For e=0, we can obtain the initial signal V The arrangement from whichthe signal is finally obtained may also be constructed as is shown inFIG. 5b. The resistor network is not provided on the cathode side of thetubes 16 and 17, but on the anode side thereof. The tapping of theresistor 45 is connected to the positive terminal of the direct-Voltagesource (not shown) and the conductor 19', from which the signal V isobtained, is connected to the junction of the identical resistors 14 and15. By displacing the tapping interpolation may be carried out betweenthe signals fed to the tubes 16 and 17.

By extending the number of supplied signals to m, m angular points arerequired, which are interconnected via m (m-l)/2 resistors, eachprovided with a tapping. The tappings are connected to the same numberof contacts of a switch 213, of which the main contact is connected tothe conductor 18.

The signal fed to the control-grid of tube 17 now has the form:

The output signal becomes:

wherein V and V designate two arbitrary signals of the series of signalsV V After conversion V is found to be:

to which again applies:

m+n2+ ln1= Further combinations are possible by connecting the tappingsof the potentiometers not to the contacts of the switch 20 but to thecontrol-electrodes of discharge tubes. With m=3, three discharge tubesare used, which constitute together an adding circuit. In the case ofFIG. 1 the output signal of this adding circuit is:

If the output signal V' is multiplied by one third, for example with theaid of a potentiometer circuit, the sum of the coefficients is alsoequal to 1, irrespective of the positions of the tappings on thepotentiometers 12, 13 and 23.

Instead of using discharge tubes, use may be made of other amplifyingelements in the arrangements described above, for example transistors.

What is claimed is:

1. A circuit for forming an output signal from a plurality of inputsignals in which the output signal is linearly dependent upon said inputsignals, said circuit comprising tapped impedance means, means applyingsaid signals to the terminals of said impedance means, means providing asum signal, said sum signal being the sum of said input signals inpredetermined proportions, first and second amplifying devices eachhaving an input electrode and an output electrode, means connecting thetap of said impedance means to one input electrode, means applying saidsum signal to the other input electrode, a tapped impedance connectedbetween said output electrodes, and output circuit means connected tothe tap of said tapped impedance.

2. A circuit for varying the coetficients determining linearrelationship between a plurality of first input signals and anadditional input signal linearily dependent upon said first inputsignals, said circuit comprising first tapped impedance means, meansapplying said first input signals to different end terminals of saidimpedance means, matrix means for deriving said additional input signalfrom said first input signals, first and second amplifying devices eachhaving an input electrode and an output electrode, means connecting thetap of said first impedance means to one of said input electrodes, meansapplying said additional input signal to the other said input electrode,second tapped impedance means connected between said output electrodes,and output circuit means connected to the tap of said second tappedimpedance means.

3. The circuit of claim 2, in which said first impedance means comprisesa network having in terminals, said terminals being interconnected byimpedances having variable taps, m being the number of said first inputsignals, said first input signals being applied to separate saidterminals, switch means for selectivein which V V ly connecting saidvariable taps to said one input electrode, said additional input signalV, has the form:

V are the input signals and 0 11 are the respective fixed coeflicients,the sum l/ -l-ip -iil/ being equal to 1, the signal V at the tap of saidsecond impedance having the form:

wherein 1 are variable coeflicients having a constant total sum of 1.

4. A circuit for correcting the brightness of an individual color of abrightness color television signal V having the form:

wherein V V and V are the individual color signals, 0,, 1,0 and 1 arethe respective fixed linear coeflicients, and 0 =1, said circuitcomprising separate sources for said individual color signals, threeresistors connected serially in a closed loop, said resistors havingvariable taps, means applying said individual color signals of the samelevel to separate junctions of said three resistors, means deriving saidbrightness signal from said individual color signals, first and secondamplifying devices each having a control electrode and an outputelectrode, means selectively connecting said Variable taps to onecontrol electrode, means applying said brightness signal to the othercontrol electrode, resistance means connected between said outputelectrodes, and output (in cuit means connected to a variable tap onsaid resistance means.

References Cited in the file of this patent OTHER REFERENCES HazeltineLaboratories Stafi, Principles of Color Television, Wiley & Sons, Inc.,July 1956, pages 412-413.

Hazeltine Laboratories Stafif, Principles of Color Television, Wiley andSons, Inc., July 1956, page 240.

